Update repositories.txt (#5840)

PIR8575, an Arduino library for 16 channel PIR detection system based upon PCF8575.

Author: RobTillaart

repositories.txt

@@ -5537,6 +5537,7 @@ https://github.com/RobTillaart/PID_RT
 https://github.com/RobTillaart/PinInGroup
 https://github.com/RobTillaart/PinOutGroup
 https://github.com/RobTillaart/PIR
+https://github.com/RobTillaart/PIR8575
 https://github.com/RobTillaart/Prandom
 https://github.com/RobTillaart/pressure
 https://github.com/RobTillaart/PrintCharArray